The present invention relates generally to the production of a laminated composite sheet material and more particularly to the production of a film paper laminated composite having transparent window portions therein.
Lamination of a plastic film material to a paper material has been found to be particularly advantageous where paper products having high strength and abrasion resistant qualities are required. Such laminated composites are particularly desirable in the packaging industry, where artwork may be printed on the interior side of the plastic film to produce a high quality display package. The construction and use of such laminated composites are described in Peer, U.S. Pat. No. 4,254,173 which is hereby incorporated by reference for all that it teaches.
In producing a laminated composite of the type described in Peer, both the plastic film material and the paper material may be provided in continuous sheets from spools. The paper and the plastic film generally pass over a number of roller type devices where each of the materials are independently stretched out under tension and treated as necessary depending upon the particular end use for the laminated composite. For example the plastic material may be irradiated in conventional processes to increase its strength or improve its printability. In preferred embodiments the plastic is printed with various graphics and provided with a metalized background over the graphics to enhance the package appearance. The paper may undergo treatment as well such as being electrostatically charged to aid in the bonding process. Either the film material or the paper material or both are treated thereafter with suitable adhesive to provide a bond between the paper and film. To complete the laminating process, the paper and film material are pressed together between opposed rollers to produce a smooth flat composite. Various heating or cooling processes may also be required to ensure proper adhesion of the surfaces, depending on the type of the film, paper, and adhesive agent which are being used in the process. The end product of the process is a laminated composite which may be fed directly to cutting dies or other machines for further processing. The composite may also be taken up directly on a separate spool for storage and later processing.
The use of paperboard containers having window portions therein is well known in the packaging industry. Using prior art packaging techniques, such windows were generally formed by first cutting a window opening in a paperboard piece, providing a transparent plastic "window pane" sheet of a size slightly larger than the periphery of the window opening, and then bonding the window pane sheet to the periphery of the window opening of the paperboard piece to form the window portion of a later assembled container. The cutting of the paperboard window opening, the cutting of the window pane sheet and gluing of the sheet to the paperboard, generally take place in a series of isolated steps which are quite time consuming in known prior art apparatus. The container packaging formed by such prior art methods, although comprising window portions, does not have the desirable physical characteristics of packaging formed from the composite material of the Peer invention due to the fact that the "window pane" material covers only an isolated portion of the package and therefore does not provide composite characteristics.
Although composite packing materials of the type described in Peer provide superior strength and esthetic display characteristics as compared to conventional paperboard packaging material, such composites were, until the present invention, unable to be produced at production line speeds with transparent window portions. A problem with window creation inherent in the production of composite material is that the adhesive used to bond the film and paper causes a discoloring of the film which is very apparent in a clear plastic window. Another problem is that the film material used in composite formation is generally printed with graphics and therefore, the windows must be provided at a fixed position relative to the graphics. A further problem lies in the fact that both the paper web and film web used in high speed composite production are to some degree extensible and difficult to align if exact registry between film portions and paper portions is required.
A need exists for a method and apparatus for producing laminated composite having transparent window portions. Such a composite should retain the superior strength and exterior display characteristics of film paper composite packaging material while providing a means for consumers to visually inspect the product enclosed within the container. The apparatus used to make a composite with window portions should be a production apparatus capable of producing the composite in a high speed cost effective manner.